Penguin fossils from 10 million to 12 million years ago have been unearthed in South Africa, the oldest fossil evidence of these cuddly, tuxedoed birds in Africa.

The new discovery, detailed in the March 26 issue of the Zoological Journal of the Linnean Society, could shed light on why the number of penguin species plummeted on Africa's coastline from four species 5 million years ago to just one today — Spheniscus demersus, or the jackass penguin, known for their donkeylike calls.

Daniel Thomas, a researcher at the National Museum of Natural History, and colleague Daniel Ksepka of the National Evolutionary Synthesis Center were studying rock sediments near a steel plant in Cape Town, South Africa, when they uncovered an assortment of fossils, including 17 pieces that turned out to be backbones, breastbones, legs and wings from ancient penguins.

The bones suggested these ancient birds ranged from 1-to-3 feet tall (0.3 to 0.9 meters). For comparison, Africa's living jackass penguin, also called the black-footed penguin, stands at about 2-feet tall (0.6 meters) and weighs between 5.5 and 8.8 pounds (2.5 and 4 kilograms). [Happy Feet: A Gallery of Pudgy Penguins]

About 5 million years ago, sea levels were 296 feet (90 m) higher than today, and the low-lying South Africa became a patchwork of islands. Those islands provided beaches for several penguin species to create nests and rear their young while sheltering them from predators.

Once the oceans fell, most of those beaches would become mainland.

Africa's remaining jackass penguins are also on the decline. Their numbers have plummeted by 80 percent, in part because humans are overfishing their staple foods, sardines and anchovies. African penguins are being bred in captivity; for instance, a successful breeding season at the New England Aquarium in 2010 ended with the birth of 11 new African penguin chicks.

In addition, Bristol Conservation and Science Foundation, along with South African and international partners, is working to establish breeding colonies of the African penguin closer to fish resources, to ensure successful chick-rearing, according to the World Association of Zoos and Aquariums.